Monolayers of several peptide lipids at air-water and air-solid interfaces were prepared using Langmuir and Langmuir-Blodgett (LB) film techniques, and tested as fluorescent sensors for copper ions in aqueous phase. In one method, both the ionophore and the fluorophore were in the same molecule (lipid A), so intramolecular interaction was responsible for the fluorescence quenching of monolayers of this lipid. In the other method, ionophore and fluorophore were located on two different molecules (lipids B and C) so the intramolecular coupling does not exist; instead the fluorescence quenching was realized by a through-space interaction mechanism. Several experimental techniques, including pi-A isotherm, epifluorescence microscopy, and absorption and emission spectroscopies were used to study the different characteristics of copper ion effect on the properties of the lipid monolayers. Additionally, the fluorescence quenching properties of the Langmuir monolayers were found to be transferred to the one-layer LB films. On LB films, the fluorescence response presented a clear selectivity for copper ions in comparison with several other transition metal ions. Further, an excellent reversibility was observed: the fluorescence was switched OFF by immersing the solid substrate in copper ion solution and ON by washing with HCl solution. The intermolecular approach used here seems to be a very flexible and general method to design surface-oriented fluorescent sensors to meet different analytic purposes.

Photo-cross-linking has received a considerable attention for the design of intelligent materials in biochemical and biomedical applications. In this report, we describe the synthesis and properties of a novel photoreversible poly(ethylene glycol)-(PEG-) based hydrogel system. 9-Anthracenecarboxylic acid was used to modify the hydroxyl groups of an eight-armed PEG polymer (molecular weight 20 000) and the degree of substitution was determined to be 87.4%. The PEG-anthracene macromers (PEG-AN) exhibited high photosensitivity at wavelengths close to visible light (absorption maxima at 366 and 380 nm) and underwent rapid and reversible photo-cross-linking upon exposure to alternating wavelengths of irradiation (365/254 nm) in the absence of photoinitiators or catalysts. Changes in light exposure and wavelength of irradiation reversibly altered the physicochemical properties of the PEG-AN hydrogel, including swellability, absorption spectrum, and topography.

Poly(ethylene glycol) (PEG) star polymer hydrogels were prepared by γ-irradiation of aqueous solutions of star PEG polymers. The swelling behavior of these gels in deionized water at 37 °C indicated that the gels prepared from PEG star polymers with a small number of long arms swelled to a greater extent than those prepared from PEG star polymers with a large number of short arms. PEG star polymers and branched PEG polymers were modified to incorporate acrylate groups on the ends of the polymer arms. These acrylated star or branched polymers were copolymerized with poly(ethylene glycol) diacrylate in the presence of UV light. The ensuing materials swelled to a greater extent than hydrogels prepared without acrylated star or branched PEG polymers. Number-average molecular weights were calculated using several rubber elasticity-based theories.

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